Vehicles, such as automobiles and trucks for example, include a driveline having a prop-shaft and a transfer-case. The prop-shaft transmits rotational energy (torque) developed by the vehicle engine to the front and rear drive modules via the transfer case. The drive modules in turn transmit the rotational energy to the wheels.
It should be appreciated that the transmission of rotational energy from the prop-shaft to the drive modules, and from the drive modules to the wheels generates reaction forces within the drive modules to counter the transmitted torque. The geometric arrangement of the driveline and drive modules is configured to reduce undesired noise and vibration that may be caused by these reaction forces. One factor that impacts noise and vibration is the angle of the prop-shaft relative to the transfer case and the rear drive module.
In some vehicles, such as off-road capable vehicles, the operator may desire to “lift” the vehicle to increase ground clearance. The lifting of the vehicle moves the vehicle chassis or frame away from the ground. This may be accomplished using several means known in the art, such as an air suspension, a hydraulic suspension, torsion bars or spacers for example. In some instances, such as air suspension and hydraulic suspension for example, the amount of lift may be actively changed by the operator.
The maximum amount of lift that may be achieved on a given vehicle is controlled at least partially by the angle of the prop-shaft. It should be appreciated that as the vehicle is lifted, the transfer case moves with the vehicle chassis away from the ground. However, the wheels and associated rear drive module remain effectively at the same vertical height. As a result, the angle of the prop-shaft will increase as the lifted height of the vehicle is increased. Therefore, the amount of lift a vehicle may achieve is limited by the angle of the prop-shaft to avoid undesired noise and vibration as well as strain on joints and seals of the transfer case and rear drive module.
Accordingly, it is desirable to provide a system that allows the vehicle lift to be actively changed by the operator while avoiding undesired noise and vibration.